The present invention pertains to a mining system and method for excavating a borehole within a mine. Specifically, the present invention pertains to a mining apparatus which implements the disclosed mining method and produces a bread loaf shaped borehole in a coal seam.
It is well known that an arch provides a stable structure that is used frequently in the construction of both bridges and dams. An arch generally provides better spanning and improved stress distribution. Because of the force distribution provided by an arch, the greater the load above the arch, the greater the compressive forces within the structure above the arch. These compressive forces lead to greater stability and security of the structure, which includes an arched shaped opening.
In underground mines, particularly coal mines, either the size of the coal seam, the type of the equipment used for mining the coal, or the need to provide space for miners to work has prevented the effective use of an arched borehole to provide stability and security within the borehole in a mine. One prior art mining machine, set forth in U.S. Pat. No. 5,553,926 issued to Blackstock et al., utilizes an elliptical cutting drum to produce a borehole having a curved roof and bottom. However, this solution tends to compromise haulage systems, which are typically configured to operate in boreholes having a flat bottom or floor. Accordingly, mines having boreholes formed using prior art methods and equipment have typically utilized a variety of different roof or ceiling supports to keep the roof or ceiling of the mine from collapsing into the borehole. As mining operations have expanded into smaller seams and have implemented more sophisticated, remotely-operated equipment, the need has arisen to utilize the stability of the arch to enhance the inherent stability and security of the borehole within a mine. The utilization of arch-shaped borehole mining techniques will provide for a deeper penetration into a mine, reduce the expense and inconvenience associated with shoring or providing support for the roof or ceiling of the borehole, and potentially allow development of coal reserves with poor roof conditions.
In addition to the need for providing stability and security for the excavated opening or borehole in the mine, there is also a need to provide a flat surface over which cutting and conveying equipment may be easily moved both to cut mining material from the face of the mine at the end of the borehole and to transport the mined material away from the face of the mine and out of the borehole to a collection point.
Underground openings with an arched top and flat bottom are not uncommon, and such designs may be observed in large underground transportation tunnels. However, because of the nature of mining operations, the size and shape of the borehole within a mine has been determined both by the shape of the reserve or ore deposit, such as a coal seam, and the space required to accommodate mining equipment. In contrast to a transportation tunnel, in which a passage is created between two points, a mining borehole is directed to the recovery of a product, namely coal, minerals and ore. As mining operations have expanded into areas previously unaccessible to human beings through the use of smaller, more sophisticated, remotely operated, computer controlled mining equipment, the desirability of creating a borehole with an arched top and flat bottom has once again become a viable consideration for designers of sophisticated mining equipment.
Accordingly, there is a need for a mining method using mining equipment that can operate in coal seams or ore deposits whose size may be too small for people to comfortably work in, which method should provide all of the structural stability and security benefits from an arched roof configuration and all of the transport and operational benefits associated with a flat floor. Such method should also enable the use of apparatus that is simple in both construction and operation.
The mining method and mining apparatus of the present invention obtains the structural and security benefits of an arched roof configuration and the transport and operational benefits of a flat floor by creating a borehole within a mine having a perimeter substantially the same as the profile or outline formed by a loaf of bread (i.e., a rounded top, flat sides and a flat bottom). Further, the present invention is less complex in operation than many other prior art mining systems.
To create a bread loaf shaped borehole, the mining method and apparatus of the present invention features the combination of four cutting systems together with three cutting support systems.
The largest of the four cutting systems is a pair of counter rotating, multi-armed cutting heads. As depicted herein, these cutting heads may have three a structural members or arms that are equally spaced apart, but it is understood that other geometries or configurations are clearly possible, such as two, four or even five armed cutting heads. These two large cutting heads use both mechanical bits and high pressure water jets, cutting independently, to remove mined material from the face of the mine and at the same time to form two large intersecting circular openings which begin to define the borehole. The cutting heads are also counter rotating so as to have the tendency to move mined material toward the center of the borehole.
Just behind the counter rotating, multi-armed cutting heads are two vertical drum-type cylindrical cutters. These two vertical drum cutters act to form both the substantially vertical walls that intersect the circular openings formed by the counter rotating, multi-armed cutting heads, and the flat, horizontal portion of the opening, which defines the floor of the borehole. The drum cutters are also counter rotating to move material toward the center of the borehole much like the multi-armed cutting heads.
Between the two vertical drum cutters and behind the pair of counter rotating, multi-armed cutting heads is a plow or scoop assembly. The plow or scoop assembly provides two functions. First, the plow or scoop assembly removes the lower kerf on the floor of the borehole produced by the cutting action of the two counter rotating, multi-armed cutting heads to create a substantially flat floor in the borehole. Second, the plow or scoop assembly guides the mined material into a funnel, chute, or gathering area. The exit end of the funnel or chute opens onto a short conveyor that is integral to the miner chassis. The conveyor transports the mined material to the rear of the mining machine and subsequently out of the borehole.
At the top of the mining apparatus, behind the two counter rotating, three-armed cutting heads is a smaller rotating cutting head, which removes the upper kerf at the top of the borehole located at the intersection of the two circular openings formed by the counter rotating, multi-armed cutting heads.
Thus, through the interaction of the two, counter rotating cutting heads, the two vertical drum cutters, the plow or scoop assembly, and the small rotating cutting head at the top of the apparatus, a borehole is formed having the shape of a bread loaf. The bread loaf shaped opening is defined by a generally arched top or ceiling, two substantially vertical side walls, and flat bottom or floor.
Enabling the described cutting system to operate are three cutting support systems. The first cutting support system is the movement or transport system, which continually moves the entire apparatus into the cutting face of the mineral seam. Second, is the conveyor system which receives the mined material falling to the floor of the borehole and then is later picked up by the plow or scoop assembly. The third cutting support system is the computer based controller system. The computer based controller system provides a variety of operational functions and may be configured to enable automatic operation of a remotely operated coal mining system.
Within the controller system are a variety of sensors that gather information regarding the motion of the system, its position and orientation within the mine, the condition and operation of the mechanical equipment, and the environmental conditions within the mine. This sensed information is then processed by the computer within the controller system to produce output signals. These output signals operate the cutting equipment, the transport system, and the conveyor system. In addition, the computer diagnoses operational problems and provides warning or shut-off signals whenever hazardous conditions occur.